In theory, a design incorporating a reusable spacecraft or booster can significantly reduce the cost of access to space. In order to realize these theoretical benefits, the launch vehicle must satisfy two design elements: 1) substantial elements of the launch vehicle and spacecraft must be reusable (either in full or in component) and 2) as costs scale with system size and complexity, the launch vehicle must be as small and simple as practicably possible.
Reusable suborbital or orbital flight hardware has been traditionally configured following two approaches. The first is to fit the reusable hardware with a precision landing system. The second is to fit the reusable hardware with a simple parachute and allow the hardware to fall to the surface. The Space Shuttle Orbiter is an example of the first approach to reusability. The orbiter features wings and landing gear; it glides to land on a long, but otherwise conventional runway. The Space Shuttle Solid Rocket Motors are an example of the second approach to reusability. After their fuel is expended, they fall into the ocean by parachute where they are later recovered.
Present approaches to reusable spacecraft and booster design do so at great impact to vehicle design. The inherent physics of a launch vehicle results in a system where only a few percentage points of the total gross-lift-off-weight are available for payload. (For example, the Space Shuttle has a net payload of less than 1.22% of its total gross-lift-of-weight). Any increase in fixed weight on the orbital or suborbital elements of a launch vehicle must be accounted for by a reduction in payload capability or an increase in the overall size of the system.
For a fixed size launch vehicle, with a small payload fraction, even a small percentage point increase in fixed weight among the heavier booster elements will radically reduce the launch vehicle's payload capacity.
For a conceptual launch vehicle, flying a design payload along an equivalent trajectory, these weight penalties of reusable systems will increase the gross-lift-off-weight in a multiplicative, rather than additive fashion.
Typical reusable technologies to enable a precision landing system (lifting bodies or wings) weigh considerably more than reusable technologies that lack precision landing capability (parachutes).
Without precision landing capabilities, reusable spacecraft and boosters are typically retrieved at sea. A water landing, resulting in salt-water immersion of space flight hardware, is detrimental to the reusability of complex space flight hardware. After an ocean recovery, only the casings of the Space Shuttle Solid Rocket Boosters can be reused. The boosters must be otherwise re-manufactured. For example, all electronics, having been exposed to the corrosive salt-water environment, must be replaced at considerable expense.
A method to ensure precision landings of reusable space launch flight hardware (either spacecraft of boosters) that would distribute heavy elements of recovery, propulsion, guidance, navigation and control to non-flight hardware could enable a radical reduction in the size, complexity and hence cost, of hardware used to launch payloads into space.
The design of recoverable and reusable spacecraft or launch vehicle (space flight hardware) elements has been well established in practice.
In U.S. Pat. No. 3,093,346, entitled “Space Capsule,” Faget illustrates a means to employ a parachute to enable the intact recovery of a returning spacecraft. A parachute is an embodiment of a concept of a lightweight, deployable membrane that provides only drag. A parachute is used to enable ballistic recovery of an object.
In U.S. Pat. No. 3,310,261, entitled “Control for Flexible Parawing,” Rogallo and Sleeman illustrate the evolution of a simple parachute into a parafoil. A parafoil is an embodiment of a concept of a lightweight, deployable membrane wing that can produce lift, drag and stabilizing forces and moments. A parafoil is used to enable the gliding recovery of an object.
The McDonnell Douglas DC-X (see: “DC-X Results and the Next Step,” AIAA 94-4674 demonstrated a concept for a reusable spacecraft using a retro-rocket system. The retro-rocket is used in lieu of a parachute to facilitate precision guidance, navigation and control for a soft landing. The DC-X featured space flight hardware where the engine is deployed and restarted after atmospheric reentry. The thrust from the engine is used to decelerate and orient the flight hardware vertically. With the rocket firing, the vehicle will then execute a precision vertical landing onto a specific landing site.
In U.S. Pat. No. 3,132,825, entitled “Space Atmosphere Vehicle,” Postle illustrates the recovery of a spacecraft or launch vehicle element through shaping of the overall configuration into a lifting body. The lifting body is an embodiment of a concept of a rigid aeroshell with surface detailing that produces lift, drag and other stabilizing forces and moments.
In U.S. Pat. No. 3,702,688, entitled “Space Shuttle Vehicle and System,” Faget teaches a more conventional approach to recovery. As found on the Space Shuttle Orbiter, this approach embodies wings and tail surfaces incorporated into the reusable flight hardware. This permits the flight hardware to glide to a landing on a conventional runway.
Examples of prior art configuration generally used to prevent a returning spacecraft lacking precision landing capabilities from destructive impact with the ground include 1) landing in water (Faget: U.S. Pat. No. 3,093,346 see above), 2) air capture using a airplane or helicopter (Mulcahy: U.S. Pat. No. 3,137,465), and 3) firing retro rockets just prior to impact (see a description of the Soyuz capsule in Handbook of Soviet Manned Space Flight, p. 119-121, ISBN 0-08803-115). In the former, the flight hardware is immersed in salt water making the design of a reusable spacecraft much more complex and heavy. In air capture, the relative size of an aircraft or helicopter to the returning flight vehicle limits its use to small capsules. This technique also is not compatible with large flight vehicles due to the potential of failed capture causing the loss of the parachute and uncontrolled descent into the ground. Retro-rockets and air bags are used to cushion the landing of the flight vehicle. In these systems, the rockets or air bags add significant weight to the flight hardware and typically do not compensate for any lateral motion at landing causing significant side loads and a possibility of roll over at landing. This leads to increased structural mass of the vehicle.
Airborne recovery of spacecraft is a hazardous operation and is not suitable for manned flight vehicles. Air capture of a returning spacecraft can cause the loss of the parachute system in a failed capture event; the spacecraft would then fall to ground at a high velocity.
A ground based recovery system that occurs at zero altitude can be man rated.
Examples of prior art configurations involving a sea based recovery platform coupled with a retro-rocket technology precision vertical landing flight hardware includes US Patent Application 2011/0017872, “Sea landing of space launch vehicles and associated systems and methods.” Here, Bezos describes a spacecraft recovery system comprising a ship fitted with a landing surface that is pre-positioned in the general reentry region. The reusable flight hardware elements, after re-entry, reorient themselves tail first, and perform a powered, vertical landing upon the ship mounted platform.
U.S. Pat. No. 2,923,504 (“Safety Landing Platform for Aircraft,” Ortega and Wallace) teaches that a system comprising an energy absorbing landing platform attached to a moving ground based vehicle may be used to simplify the landing gear design of an airplane. While this patent describes a vehicle that is in motion at the time of capture, the wheeled has only limited steering capability.
Hovercraft are air cushion vehicles, employing the principle of aerodynamic levitation of a structure above a surface. McCreary in U.S. Pat. No. 3,532,179, entitled “Aerodynamic Lifting Device and Method of Lifting,” where the air cushion is formed by means of a flexible, pneumatically stabilized diaphragm underlying the vehicle, teaches the design principles of a modern hovercraft.
All of the above references are hereby incorporated by reference.